When Issac Newton gave his equations on gravity to the world, there were certain individuals who theorised on gravity's internal effects on stars.The first known individual to suggest super-massive stars was the 18th-century English rector John Michell. He was Cambridge educated and an avid astronomer. In 1783, Michell wrote a letter to Henry Cavendish, the discoverer of hydrogen, suggesting that there could be "dark stars" so massive that "all light emitted from such a body would be made to return towards it, by its own proper gravity." In 1796, the French astronomer, Pierre Laplace, independently said much the same thing. The existence of super-dense stars took a back seat in astrophysics until Einstein presented his general theory of gravity, published in 1916. Einstein ignored the possibility of infinitely dense "singularities" in his equations, but the German astronomer, Karl Schwarzschild, was intrigued by them. Schwarzschild calculated that when a star collapses to a certain size, space-time breaks down. Einstein wasn't impressed and said that Schwarzschild had got his equations wrong.In 1930, aged 19, Subrahmanyan Chandrasekhar, while sailing to a new life from India to Britain, calculated that stars with a mass at least 1.4 times the solar mass would collapse indefinitely.In the 1960s, "dark stars" or "singularities" were renamed and popularised as black holes by American astrophysicist, John Wheeler. Stephen Hawking was fascinated with Wheeler's black hole research. Hawking calculated that black holes should evaporate, a process now referred to as "Hawking radiation". Black hole nomenclature now consists of the "Schwarzschild radius", the "Chandrasekhar limit" and "Hawking radiation".Indirect evidence for black holes has existed for some time, due to their gravitational effects on nearby stars. The first image of a black hole would have delighted the black hole pioneers, with the possible exception of Einstein, who didn't think that such bodies could exist.

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Last edited by brian livesey on Fri May 17, 2019 9:42 am, edited 1 time in total.

BrianThanks for your piece on Black Holes. I must admit there are some (arguably many!!!) aspects of astronomy (& particularly cosmology) that seem completely beyond my understanding.But I now try not to worry about them too much.Best wishes from Cliff

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